1. Technical Field
The present disclosure relates generally to a method of controlling a phase-shift full-bridge converter, and more particularly to a method of controlling a phase-shift full-bridge converter in a light load operation.
2. Description of Related Art
With the development of the semiconductor technology, the trend of designing small, short, thin, and light electronic products is necessary. For the power electronic products, the switching frequency is continually increased in order to effectively reduce volume and weight of the switching power converter. However, the power switch components of the power converter withstand higher switching stresses and also produce more switching losses, once the switching frequency is increased, thus reducing the conversion efficiency of the switching power converter.
Because the conventional switching power converter is operated by the hard switching technology, the switching losses of the power switch components are also with increased if the switching frequency is increased. Therefore, the switching losses would reduce the conversion efficiency, shorten the use life of the switch components, and increase the occupied space and costs of the additional heat-dissipating devices. In addition, the voltage or current surge produced due to the non-ideal switching behavior causes the electromagnetic interference (EMI).
In order to overcome problems caused due to the high-frequency, the soft switching technology is applied to a variety of power electronic products. The soft switching is generally divided into two categories: zero voltage switching (ZVS) and zero current switching (ZCS). ZVS technology means that the voltage difference across two terminals of the power switch component is decreased to zero during the transient period and then the power switch component is turned on. In other words, a product of the voltage difference and the current flowing the power switch component is zero so as to reduce switching losses of the power switch components, restrain the voltage and current surge, increase conversion efficiency and circuit stability, and reduce noise interference and electromagnetic interference.
In addition, there are two possible conditions would occur in the light load operation of the PSFB converter: (1) the resonance energy is insufficient due to the small current at resonance points when the output inductor current is in the continuous conduction mode (CCM); (2) the resonance energy is zero due to zero current at resonance points when the output inductor current is in the discontinuous conduction mode (DCM).
Accordingly, it is desirable to provide a method of controlling a PSFB converter in a light load operation to implement the optimal degree of soft switching the power switches so as to improve the overall efficiency, reduce switching losses, and achieve the electromagnetic compatibility.